Crown liner technology
Current crown liner technology includes the in situ molding of a thermoplastic liner material directly in the crown which will later be used for bottling beer or other beverages. Such liners are primarily made of polyvinyl chloride ("PVC") in the United States and of thermoplastics that do not contain chlorine, such as EVA or polyethylene ("PE"), in Europe and Japan. A conventional apparatus for making lined crowns is the Za-Matic.RTM. Model 1400A (available from ZapatA Industries, Inc.) described in U.S. Pat. Nos. 3,135,019, 3,360,827, and 3,577,595. The liner compositions may be based upon plastics such as, for instance, PVC, EVA, or PE, and may include those of U.S. Pat. No. 3,547,746.
PVC compositions with or without additives as stabilizers or for imparting certain properties are known in the art. For instance, U.S. Pat. No. 4,380,597 discloses a stabilized thermoplastic composition of PVC or mixed polymers that may include ascorbates or gluconates as stabilizer additives. These stabilizers are added not to absorb oxygen from inside packages made of the polymer but to prevent breakdown of the polymer itself. U.S. Pat. No. 4,211,681 discloses shaped articles, for instance films or tubes, that include high molecular weight poly(ethylene oxide) polymers with stabilizers of ascorbic acid, 2,3-butylhydroxyanisoles, and the like. Japanese Patent Application No. 62-215,101 discloses a deodorizing fiber obtained by treating thermoplastic fibers with inorganic particles of divalent ferrous iron and L-ascorbic acid. U.S. Pat. No. 4,278,718 discloses a sealing composition for beverage containers consisting of a vinyl chloride resin, a plasticizer, and a metal oxide.
The liners for most beverage closures are based either on PVC or EVA, although other materials have been used too. For instance, U.S. Pat. No. 4,968,514 teaches that polyurethanes can be used to make liners for metal-shelled beer bottle crown caps. These polymer bases can be compounded to give adequate processing properties and product performance, utilizing among other additives heat stabilizers, antioxidants, and lubricants. Naturally occurring fatty acids are often used as lubricants in liner formulations. Fatty acids are separated into individual products and purified by distillation. Because of the wide range of individual acids occurring in nature, a distillation fraction will contain several fatty acids. Some of the impurities contain unsaturation at the 4-, 5-, 6-, 7-, or 8-carbon position. The fatty acids are converted to ester or amide derivatives which likewise contain mid-chain unsaturation. When used as lubricants in liner formulations, the fatty acid derivatives are subject to oxidation at the mid-chain unsaturation by oxygen or other oxidizing agents in the beverage or in the air that is enclosed along with the beverage in the container. Such oxidation results in aldehydes, some of which have very low flavor thresholds. Such liners, however, are adequate for many beverage products in that their contribution of off-flavor to the beverage is not noticeable.
Some beverages, though,--notably, mineral waters--have such delicate bouquets that they cannot tolerate even the relatively slight off-flavors that can be generated with conventional liners. The polymeric cap liner of the container is a source of double-bond containing precursors that react with oxygen in bottled water. Polymeric cap liners typically contain a number of plasticizers, heat stabilizers, lubricants, antioxidants, blowing agents, and pigments, some or all of which contain double bonds that are susceptible to attack by oxygen. For example, the liner formulations for twist-off caps typically comprise oleamide-type lubricants. The double bonds in such oleamides are readily susceptible to attack by oxygen, resulting in off-flavored producing medium-chain-length aldehydes. Also, fatty acids or derivatives of fatty acids of liner compositions react with oxygen to form off-flavored aldehydes. Other compounds often found in polymeric cap liners which are susceptible to attack from oxygen include activated aromatic compounds such as phenols, and other double bond containing compounds such as ketones, amides, erucic acid, etc. The resulting aldehydes are responsible for the fruity tastes and odors often found in bottled water.
While one solution to this problem is to remove the compounds that are reactive with oxygen, this solution is not practical since the liner would not possess the desired properties to properly seal the bottle. While the presence of off-flavor substances may be more readily remarked in water than in more strongly flavored beverages such as beer, the presence of such substances can adversely affect the taste of the more strongly flavored beverages. Accordingly, a need exists for an improved liner which can protect against the development of an off-flavor in bottled water or other fluids.
Oxygen-related problems in beer generally
In packaging oxygen-sensitive materials such as foodstuffs, beverages, and pharmaceuticals, oxygen contamination can be particularly troublesome. Care is generally taken to minimize the introduction of oxygen or to reduce the detrimental or undesirable effects of oxygen on the product. Carbon-carbon double bonds are particularly susceptible to reaction with active oxygen species. Such carbon-carbon bonds are often found in foods and beverages, pharmaceuticals, dyes, photochemicals, adhesives, and polymer precursors. Virtually any product that has complex organic constituents will contain such carbon-carbon double bonds or other oxygen-reactive components, and hence can undergo oxidative reactions.
Where the products of the oxidative reactions adversely affect the performance, odor, or flavor of the products, then removing the oxygen which is present (either dissolved in or trapped with the product), preventing oxygen ingress, and inhibiting the reactions of oxygen will all benefit the product. A number of strategies exist to deal with oxygen as a contaminant. The most basic is simply to remove oxygen from the product by vacuum, by inert gas sparging, or both. Such systems are used in boiler water treatment, in the orange juice and brewing industries, and in modified-atmosphere packaging of food products. This technology, while somewhat equipment intensive, can remove up to 95% of the oxygen present in air from the product or its container prior to or during packaging. However, removal of the remaining oxygen using this approach requires longer times for vacuum treatment and/or sparging and increasingly larger volumes of higher and higher purity inert gas that must not itself be contaminated with trace levels of oxygen. This makes the removal of the last traces of oxygen very expensive. A further disadvantage of these methods is a tendency to remove volatile product components. This is a particular problem with foods and beverages, in which such components are often responsible for much of the aroma and flavor.
In beer, for instance, it has been known since the 1930's that oxygen in beer adversely affects it flavor and stability. Amounts of oxygen as low as 0.1 to 0.2 ml per 355 ml container will, over time, cause darkening of the beer, an increase in chill-haze values, and significant taste changes. Oxygen's effect on beer is so strongly detrimental that many brewers go to great lengths to remove it from the bottle during the filling process. One usual technique is to remove the air via vacuum from a clean bottle, fill the bottle with carbon dioxide, flow the beer down the bottle wall into the bottle thus displacing the carbon dioxide, and finally squirting a jet of high-pressure deoxygenated water into the bottle to cause the beer to over-foam just as the cap is put on, thereby attempting to displace the remaining headspace gases with the beer's own carbon dioxide. In addition, production lines are run slowly in order to minimize the introduction of air into the headspace just before capping. All of this is expensive, and usually reduces the total oxygen concentration in the headspace to about 200-400 parts per billion. The 200-400 ppb achieved in the packaged product by careful brewers corresponds to approximately 50-100 microliters of oxygen per 355 ml bottle. Even this small quantity of oxygen is still considered to be one of the major limitations on quality and shelf life of beer today. The desired level is as close to zero as possible, but certainly below about 50 ppb.
Prior art oxygen scavenging
None of the above techniques remove or control oxygen that is dissolved in the product or leaked or permeated into the package. Compounds such as sulfur dioxide, trihydroxybutyrophenone, butylated hydroxy toluene, butylated hydroxy anisole, ascorbic acid, isoascorbic acid, and glucose oxidase-catalase have been used in an attempt to reduce the effects of oxygen when it is dissolved in beer. See, for instance, Reinke et al., "Effect of Antioxidants and Oxygen Scavengers on the Shelf-Life of Canned Beer", A.S.B.C. Proceedings, 1963, pp. 175-180; Thomson, "Practical Control of Air in Beer", Brewer's Guild Journal, Vol. 38, No. 451, May 1952, pp. 167-184; von Hodenberg, "Removal of Oxygen from Brewing Liquor", Brauwelt International, III, 1988, pp. 243-4.
The direct addition of such agents into beer has several disadvantages. Both sulfur dioxide and ascorbates, when added to beer, can result in production of off-flavors, thus negating the intended purpose of the addition. Many studies have been conducted on the effect of such agents on the flavor of beer. See, for instance, Klimowitz et al., "The Impact of Various Antioxidants of Flavor Stability", MBAA Technical Quarterly, Vol. 26, 1989, pp. 70-74; Gray et al., "Systematic Study of the Influence of Oxidation on Beer Flavor", A.S.B.C. Proceedings, 1948, pp. 101-112. Also, direct addition of such compounds to a food or beverage requires stating on the label that the product contains the additive--an undesirable matter with today's emphasis on "freshness" and "all natural" products.
Attempts have been made to incorporate oxygen scavenging systems in a container crown or closure. For instance, U.S. Pat. No. 4,279,350 discloses a closure liner that incorporates a catalyst disposed between an oxygen-permeable barrier and a water-absorbent backing layer. U.K. Patent Application No. 2,040,889 discloses a closure in the form of a stopper molded from ethylene vinyl acetate ("EVA") having a closed-cell foamed core that may contain water and sulfur dioxide to act as an oxygen scavenger and a liquid-impervious skin. European Patent Applications Nos. 328,336 and 328,337 disclose container closure elements, such as caps, removable panels, liners, or sealing compositions that are formed of a polymeric matrix containing an oxygen scavenger therein. U.S. Pat. No. 4,287,995 discloses a sealing member for a container that is used to preserve aqueous liquids therein. This sealing member is mounted on the cap or stopper of the container on the portion facing the contents. The sealing member contains an oxygen absorbent that is separated from contacting the contents of the container by a film that has a plurality of fine openings such that it is gas-permeable but water-impermeable at one atmosphere pressure.
U.S. Pat. No. 5,143,763 describes an approach that prevents oxygen deterioration in containerized substances that relies on the absorption of oxygen from within the container. This patent does not teach how to prevent the containerized substances from developing off flavor that is due to leaching substances from the liner.